Milk protein genetic variants have been shown to be associated with milk production traits and manufacturing properties of milk. Selection for milk protein genotypes, therefore, might contribute to improvement of dairy cattle. Selection for x-casein and yff-lactoglobulin genotypes might be of potential interest because of their effect on milk production traits and cheese production, respectively. The aim of the present study was to quantify the effects of selection for x-casein and jS-lactoglobulin genotypes by using stochastic simulation of a closed adult MOET nucleus breeding scheme. After 11 generations of selection for x-casein genotypes in addition to selection for phenotypic milk production information, selection response was increased by 0.114 crp over the selection response by selection for phenotypic milk production information only. The annual genetic progress was increased by 4.8% in the first seven generations. The additional response obtained by including y?-lactoglobulin genotypes was 0.081 ap and the annual genetic progress was increased by 3.9% in the first seven generations. These results were obtained assuming the effects of milk protein genotypes to be known without error. If estimated effects are inaccurate the additional response of selecting for x-casein or yS-lactoglobulin genotypes is lower. Additional gain for both milk protein genes was due to increased selection intensity on the male side.

Henk Bovenhuis, J. MI de Boer

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 311–318, 1994
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